Three-dimensional Finite Element Computation of Eddy Currents in Synchronous Machines

Doktorsavhandling, 1998

The thesis deals with the computation of eddy-current losses in the end regions of synchronous machines. Various magnetic and electric vector potential formulations of three-dimensional eddy-current problems are investigated. The equations are discretized by the finite element method with nodal or edge finite elements. Special attention is given to modeling the windings of electrical machines and their contribution to the magnetic field. Two benchmark problems are used to compare the different formulations and finite elements. Hexahedral edge finite elements give more accurate results for a given discretization than nodal finite elements and allow for a reduction of the computational effort necessary to achieve a given accuracy. The accuracy obtained by the different vector potential formulations is roughly the same. An end-region model of a hydrogenerator running at no load has been studied; the magnetic flux densities as well as the eddy-current losses obtained by the different formulations and finite elements have been in good agreement with each other. The end region of a turbogenerator has been investigated in no-load and rated-load operations. The results show that in the end region, the calculated eddy-current losses at load are almost twice those at no load. A synchronous motor with solid pole shoes has been studied during starting, and extensive measurements of the temperature and the magnetic flux density in the end regions have been carried out.